This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-24418 filed on Jan. 31, 2002.
1. Field of the Invention
The present invention relates to a fuel vapor processing device of an internal combustion engine, which adsorbs fuel vapor vaporized in a fuel tank into a canister and then purges it by discharging it into an intake passage of the internal combustion engine based on a current operational state of the internal combustion engine.
2. Description of Related Art
A previously proposed fuel vapor processing device of an internal combustion engine uses a canister filled with activated carbon as the adsorption material to adsorb and retain fuel vapor vaporized in a fuel tank while a vehicle is running or stopped to substantially restrain release of the fuel vapor from the vehicle to the atmosphere. The fuel vapor temporarily adsorbed and retained in the canister is desorbed by outside air, which is suctioned into the canister through a canister atmosphere communicating orifice by a vacuum developed in the intake passage upon operation of the internal combustion engine. Then, the desorbed fuel vapor is discharged into the intake passage. Thereafter, the fuel vapor is mixed with air introduced into the intake passage together with fuel injected by an injector (fuel injection valve) to form a predetermined air-fuel mixture, which is then supplied into a combustion chamber in the internal combustion engine for combustion.
In recent years, regulations regarding discharging fuel vapor into the atmosphere are being tightened. For example, the ORVR (Onboard Refueling Vapor Recovery) regulation requires that fuel vapor escaping from the fuel tank during refueling is completely captured in a canister without discharging it into the atmosphere. Therefore, a large amount of fuel vapor must be processed in the canister, creating a demand for a canister with better performance. The adsorption and desorption performance of activated carbon is greatly affected by temperature. That is, the adsorbed fuel amount increases as the temperature drops, and the desorbed fuel amount increases as the temperature rises. Furthermore, the canister interior temperature rises during adsorption, and the canister interior temperature falls during desorption. Thus, the activated carbon performance is not fully realized.
Japanese Unexamined Patent Publication No. 2001-182632 discloses a fuel vapor processing device that addresses this problem to improve desorption performance. In the fuel vapor processing device, a heater is arranged on an exterior wall of the canister or in the center of the canister to heat the activated carbon during desorption of the adsorbed fuel from the canister. Although a temperature range for achieving an effective result of temperature adjustment is considered, a structure of the fuel vapor processing device is disadvantageously complicated, and a cost of the fuel vapor processing device is disadvantageously increased due to the use of an HC concentration sensor for monitoring a concentration of purge fuel vapor (purge gas) and a temperature sensor in the heater temperature adjustment control process.
The present invention addresses these disadvantages. Thus it is an objective of the present invention to provide a fuel vapor processing device for an internal combustion engine, which has a simple structure and is capable of performing favorable fuel vapor processing without using an HC concentration sensor to monitor the purge fuel vapor (purge gas) concentration in heater temperature adjustment control process.
To achieve the objective of the present invention, there is provided a fuel vapor processing device for an internal combustion engine. The fuel vapor processing device includes a canister, a purge control means, a temperature adjusting means and an activation control means. The canister includes a case and a fuel adsorption layer, which is received in the case and includes an adsorption material for adsorbing fuel vapor. One end of the case is communicated with a fuel vapor passage connected to a fuel tank and is also communicated with a purge passage connected to an intake passage of the internal combustion engine. The other end of the case is communicated with the atmosphere. The purge control means is for enabling temporary adsorption and retainment of fuel vapor, which is released from the fuel tank to the fuel vapor passage, in the fuel adsorption layer and for enabling desorption and conduction of the fuel vapor from the fuel adsorption layer into the intake passage through the purge passage during operation of the internal combustion engine. The temperature adjusting means is for adjusting the temperature of the fuel adsorption layer. The activation control means is for controlling activation and deactivation of the temperature adjusting means based on an adsorbed amount of fuel vapor adsorbed and retained in the fuel adsorption layer.